DO NOT do this. The problem is with the asserts, you are getting a status 7 error because 4.3 ROM's don't recognize the new bootloader. Following advice that involves "I don't remember..." and "I think..." can be a good way to gain a fancy new paperweight, especially when Knox is involved. And no, Knox does not stop rooting, the latest SuperSU .zip file is all that is needed, once custom recovery is installed, in order to gain root. From the OP, it sounds like gaining root is not the issue anyway, the issue is that the new MK3 bootloader is not listed in the old updater-script assert checks which are included on any custom AOSP ROM based on 4.3 prior to the official update.
To the thread author: this is a good example of why being much more specific in the OP would save a lot of trouble, instead of a vague "Please help" message. Specifics allow other users the chance to offer valid advice instead of playing Twenty Questions and risking harmful answers.